Known, commonly commercially available cleaning solutions that have sterilizing activity include those containing, as the primary component, 1) aqueous hydrogen peroxide solution, 2) sodium chlorite, 3) sodium hypochlorite, and the like. Due to ease of handling or other reasons, those mainly containing sodium hypochlorite are widely used as cleaning solutions that have general sterilizing activity.
Such a cleaning solution is typically produced for use by diluting a high concentration of commercially available stock solution. These cleaning solutions are in widespread use in applications such as disinfectant solutions for hospitals, dental clinics, and the like, and as cleaning solutions for home use, as sterilizing agents, bleaching agents, and oxidizing agents. However, a stock solution adjusted so as to have a high concentration is a strong alkali, meaning that it has a high pH, and is thus hazardous upon contact with the skin etc. In addition, dilution of a stock solution to a suitable pH level causes evolution of chlorine gas and the like, thereby requiring great care. Moreover, problems of toxicity, odor, and other properties thereof always pose problems in storage and management of the chemical solutions.
A sterilizing cleaning process is required in many situations in hospitals and in other facilities, and automatically-controlled conditioning apparatuses for disinfectant solution mainly containing sodium hypochlorite are also available. However, introduction of such large-scale apparatus is limited by cost and floor area, and is thus difficult.
Thus, when a sodium hypochlorite solution generally for sterilization is used as a disinfectant solution, a technique that adjusts the pH, and a technique that uses diaphragm-free or diaphragm-based electrolysis, both after dilution of an aforementioned chemically-synthesized solution, are known (Patent Literature 1).
For producing sodium hypochlorite by electrolysis process, a diaphragm-free and diaphragm-based techniques described above are known. When sodium hypochlorite is produced using a diaphragm, the negative electrode chamber and the positive electrode chamber are separated from each other by the diaphragm, permitting high concentrations of chlorine and alkali hydroxide to react with each other. Accordingly, such method is used in large-scale production of alkali hydroxide and chlorine (Patent Literatures 2, 3, and 4).
However, since the aforementioned method involves handling of a solution containing high concentrations of chemical agents, a dedicated facility is required, which leads to complexity.
Therefore, for production of a sodium hypochlorite solution on a small scale or for home use, a production method by electrolysis of common salt etc. and water using a diaphragm-free process is known. Although the sodium hypochlorite solution produced using the aforementioned method contains a lower concentration of sodium hypochlorite than the concentration of one produced using a diaphragm-based electrolysis technique, bleaching and sterilization can be sufficiently provided. In addition, the method using a diaphragm-free process is advantageous in that production facilities can be provided with a simpler structure.
As also described above, sodium hypochlorite (NaClO) has previously been known as having sterilization efficacy, and it has previously been known that hypochlorous acid (HClO) generated by hydrolysis is the sterilizing component.
It is known that effective chlorine greatly changes its form depending on the pH level. Since it is thought that hypochlorous acid, which provides high sterilization efficacy, rapidly decreases its existing ratio by changing into hypochlorite ions (OCl—) having low sterilizing ability when the pH exceeds 7, and also taking into consideration of preventing evolution of chlorine gas in a strongly acidic pH range, a sterilizing solution is typically adjusted to a value from 3 to 7, in which hypochlorous acid is said to be present in a high existing ratio (Patent Literature 1)
Thus, a generally-used neutral sterilizing solution for dental unit has a pH of from 6.5 to 7.0, and an effective chlorine concentration of from 10 to 40 ppm. A hypochlorous acid solution used for general disinfection or other purpose also has a pH of as low as from 2.2 to 7.5, and an effective chlorine concentration of as low as from 10 to 100 ppm.
However, an affected area in the oral cavity is usually covered with a smear primarily formed of protein. This presents a problem in that, without changing the conditions, application of a sterilizing solution having a predetermined pH concentration that provides sterilizing effects would not allow the sterilizing solution to act directly on the affected area by being blocked by the protein or the like covering the surface of the affected area. Another problem is that even if the sterilizing solution is applied, reaction with a smear (protein etc.) on the affected area and/or with a smear (protein etc.) in a tube of the dental unit prevents sufficient sterilizing ability from being achieved at a predetermined pH that provides sterilizing activity.